From the past, a method is proposed for repetitively controlling a voltage, current so as to cancel a changing in speed due to a changing in load torque, as a method for controlling a motor for driving a periodical load so as to suppress changing in its rotation speed.
When this method is employed, and when fidelity is improved, a disadvantage arises in that instability is realized in higher harmonics. On the contrary, when fidelity is lowered, a disadvantage arises in that shifting in phase is realized.
When fidelity is improved, a disadvantage arises in that the current becomes too great, power devices and a motor with great capacity should be employed, thereby increase in cost is realized.
Further, a method is also proposed for detecting a rotor position of a motor based upon the detection values for voltage and current and the instrument constants of the motor, without employment of a rotary encoder or the like. As the instrument constants, determined values are used as they are, or values adjusted at the manufacturing timing are used. Therefore, a disadvantage arises for the former case in that an area is generated due to the changing of the instrument constants, within the area the motor cannot be driven. A disadvantage arises for the latter case in that increase in cost is realized.
Particularly, when the voltage and current are controlled so as to cancel speed changing due to load torque changing, a disadvantage arises in that the processing for detecting a rotor position of a motor is possibly diverged.
The present invention was made in view of the above disadvantages.
It is an object of the present invention to offer a motor controlling method and apparatus thereof which can improve stability and can realize decrease in cost when a voltage and current are controlled so as to suppress speed changing due to load torque changing.
It is another object of the present invention to offer a motor controlling method and apparatus thereof which can improve rotor position detection accuracy by identifying the instrument constants when a rotor position of a motor is detected based upon detection values for voltage and current and the instrument constants of the motor without using a rotary encoder or the like.